We wish to complete the measurement of parameters relevant to aggregation in D. discoideum, NC-4 (wild-type). We shall continue to characterize and test aggregation-defective mutants already collected in strain FGR-23 and others. We shall collect further aggregation-defective mutants in strain FGR-23. These will be characterized according to their phenotypes, and to defects in the competencies required for aggregation, by a variety of screening techniques. We shall assign the mutations to complementation groups using established methods for cell fusion to produce diploids from the haploid amoebae. We shall assign the complementation groups to linkage groups, using selective methods based on ts, drug resistance and morphological markers, both obtained by others and by ourselves. Finally, we shall map the relative positions of complementation groups using recombination from mitotic crossing over and several markers on each linkage group.